Integrated circuit capacitor including anchored plug

ABSTRACT

An integrated circuit capacitor includes a substrate with an interconnection line adjacent the substrate, and a first dielectric layer on the interconnection line. The first dielectric layer includes a trench therein. The metal plug includes a body portion extending upwardly into the trench, and an anchor portion is connected to the body portion and extends into the interconnection line. The anchor portion has an enlarged width portion to anchor the metal plug adjacent lower portions of the first dielectric layer. Because the metal plug is anchored, a depth of the trench can be greater without the metal plug becoming loose and separating from the underlying interconnection line.

RELATED APPLICATION

This application is based upon prior filed copending provisionalapplication No. 60/117,186 filed Jan. 26, 1999, the entire disclosure ofwhich is incorporated herein by reference.

FILED OF THE INVENTION

The present invention relates to the field of semiconductor devices,and, more particularly, to a capacitor.

BACKGROUND OF THE INVENTION

Capacitors are used extensively in electronic devices for storing anelectric charge. A capacitor includes two conductive plates orelectrodes separated by an insulator. The capacitance, or amount ofcharge held by the capacitor per applied voltage, depends upon the areaof the plates, the distance between them, and the dielectric value ofthe insulator. Capacitors may be formed within a semiconductor device,such as, for example, a dynamic random access memory (DRAM) or anembedded DRAM.

As semiconductor memory devices become more highly integrated, the areaoccupied by the capacitor of a DRAM storage cell shrinks, thusdecreasing the capacitance of the capacitor because of its smallerelectrode surface area. However, a relatively large capacitance isdesired to prevent loss of stored information. Therefore, it isdesirable to reduce the cell dimension and yet obtain a highcapacitance, which achieves both high cell integration and reliableoperation.

One technique for increasing the capacitance while maintaining the highintegration of the storage cells is directed toward the shape of thecapacitor electrodes. In this technique, the polysilicon layer of thecapacitor electrodes may have protrusions, fins, cavities, etc., toincrease the surface area of the capacitor electrode, thereby increasingits capacitance while maintaining the small area occupied on thesubstrate surface.

Instead of forming the capacitor on the substrate surface, capacitorsare also formed above the substrate, i.e., they are stacked above thesubstrate. The surface area of the substrate can then be used forforming transistors With respect to increasing the capacitance of astack capacitor, U.S. Pat. No. 5,903,493 to Lee discloses a capacitorformed above a tungsten plug. The surface area of the capacitor isincreased by etching a trench in the dielectric layer around thetungsten plug. The tungsten plug interfaces with an underlyinginterconnection line, thus allowing different layers formed above thesubstrate to be connected.

The trench is patterned by conventional etching or other suitabletechniques. The fundamental limit on how far the trench can be etched isdetermined by how well the tungsten plug is anchored or secured withinthe dielectric layer. Typically, the depth of the trench is limited toabout one half the thickness of the dielectric layer. After the trenchhas been etched, a capacitor is formed above the tungsten plug.Unfortunately, if the trench is etched beyond one half the thickness ofthe dielectric, the tungsten plug is more likely to become loose andfall out. This physical separation between the tungsten plug and theunderlying metal interconnection with the interconnection line can causeopen circuits to be formed resulting in complete failure of the deviceor circuit incorporating the capacitor.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to increase the capacitance of a capacitor withoutreducing the reliability thereof.

This and other advantages, features and objects in accordance with thepresent invention are provided by an integrated circuit capacitorcomprising a substrate, a first dielectric layer adjacent the substrateand having a trench therein, and a metal plug anchored to the firstdielectric layer. More particularly, the metal plug preferably includesa body portion extending upwardly into the trench, and an anchor portionconnected to the body portion and extending into an underlyinginterconnection line. The anchor portion preferably has an enlargedwidth portion to anchor the metal plug adjacent lower portions of thefirst dielectric layer. The body portion and the anchor portion arepreferably formed as a monolithic unit.

Because the metal plug is anchored, a depth of the trench can be greaterwithout the metal plug becoming loose and separating from the underlyinginterconnection line. If this were to occur, an open circuit would occurresulting in failure of the device or circuit incorporating theintegrated circuit capacitor. The anchor portion of the metal plug thusallows the depth of trench to be increased to thereby increase thecapacitance, and without reducing the reliability of the integratedcircuit capacitor.

The capacitor also preferably includes first and second electrodes and asecond dielectric layer therebetween. The first electrode lines thetrench and contacts the metal plug. The second dielectric layer overliesthe first electrode, and the second electrode overlies the seconddielectric layer. Increasing the depth of the trench in accordance withthe present invention increases the surface area of the first and secondelectrodes. This advantageously increases the capacitance of thecapacitor, which is desired for preventing a loss of stored information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an integrated circuit capacitorincluding an anchored metal plug in accordance with the presentinvention.

FIGS. 2-5 are cross-sectional views illustrating the process steps formaking an integrated circuit capacitor including an anchored metal plugin accordance with the preset invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout The dimensions of layers andregions may be exaggerated in the figures for greater clarity.

Referring initially to FIG. 1, a crosssectional view of an integratedcircuit capacitor 20 including an anchored metal plug 32 is nowdescribed. The integrated circuit capacitor 20 is formed on a substrate24 with an interconnection line 26 adjacent the substrate, and a firstdielectric layer 28 is on the interconnection line. The first dielectriclayer 28 includes a trench 30 therein. The trench 30 is formed adjacentthe metal plug 32 allowing the capacitor 20 to occupy a greater surfacearea, thus increasing its capacitance.

The metal plug 32 includes a body portion 34 extending upwardly into thetrench 30, and an anchor portion 22 connected to the body portion andextending into the interconnection line 26. The anchor portion 22 has anenlarged width portion 23 to anchor the metal plug 32 adjacent lowerportions of the first dielectric layer 28. Because the metal plug 32 isanchored, a depth d of the trench 30, for example, can be greater thanhalf the thickness of the first dielectric layer 28 without the metalplug becoming loose and separating from the underlying interconnectionline 26. If this were to occur, an open circuit would occur resulting infailure of the device or circuit incorporating the integrated circuitcapacitor 20.

The integrated circuit capacitor 20 includes first and second electrodes36, 40 and a second dielectric layer 38 therebetween. The firstelectrode 36 lines the trench 30 and contacts the metal plug 32. Thesecond dielectric layer 38 overlies the first electrode 36, and thesecond electrode 40 overlies the second dielectric layer. Assemiconductor devices become more highly integrated, for example, anembedded dynamic random access memory (EDRAM), the capacitance of acapacitor would otherwise decrease because of its smaller availableelectrode surface area. However, a relatively large capacitance isdesired to prevent loss of stored information. Therefore, increasing thedepth d of the trench 30 in accordance with the present inventionincreases the surface area of the first and second electrodes 36, 40.This advantageously increases the capacitance of the capacitor 20.

The illustrated interconnection line 26 is a multilayer interconnectline formed on an insulating layer 42. The insulating layer 42 is formedon or above the semiconductor substrate 24. The semiconductor substrate24 contains a plurality of active devices, such as transistors, whichare connected together into functional circuits by the interconnectionline 26.

The illustrated multilayer interconnection line 26 includes a conductivecapping layer 44, a conductor portion 46, and an electromigrationbarrier layer 48. The conductive capping layer 44 and theelectromigration barrier layer 48 are preferably a refractory metalcompound; and the conductor portion 46 is preferably an aluminum orcopper alloy, for example. Additionally, an anti-reflective coating(ARC) 50, such as titanium nitride, may be formed on the interconnectionline 26.

The integrated circuit capacitor 20 is electrically connected to theinterconnection line 26 by the metal plug 32. The metal plug 32preferably comprises tungsten or any suitable, electrically conductivematerial such as aluminum, titanium or titanium nitride. An importantfeature of the present invention is that the metal plug 32 is anchoredadjacent the lower portions of the first dielectric layer 28 to preventthe plug from becoming loose and separating from the underlyinginterconnection line 26. The metal plug 32 has a body portion 34 havinga first width which extends through the first dielectric layer 28, theARC layer 50, and the capping layer 44. The enlarged width portion 23 ofthe anchor portion 22 has a second width wider than the first width. Theenlarged width portion 23 of the anchor portion 22 preferably has aconvex shape. However, other shapes are acceptable as long as theenlarged width portion 23 extends beyond the body portion 34 of themetal plug 32.

The anchor portion 22 is formed within and surrounded by theinterconnection line 26. In other words, the anchor portion 22 does notrest on the outer surface of the interconnection line 26. The enlargedwidth portion 23 of the anchor portion 22 undercuts the capping layer 44of the interconnection line 26 within a range of about 100 to 600angstroms. The amount of undercutting must be sufficient to anchor thebody portion 34 of the metal plug 32 while still allowing high densityplacement of other metal plugs above the semiconductor substrate 24. Awidth of the body portion 34 of the metal plug 32 is typically in arange of about 1,000 to 3,500 angstroms. The relationship of theenlarged width portion 23 of the anchor portion 22 to the width of thebody portion 34 of the metal plug 32 is such that the enlarged widthportion is greater than about 10% of the width of the body portion 34.

Additionally, the anchor portion 22 extends to a depth beneath thecapping layer 44 sufficient to lock the body portion 34 of the metalplug 32 securely in place. The anchor portion 22 also does not extendinto the electromigration shunt layer 50 so that the electromigrationresistance of the interconnection line 26 is impeded. The metal plug 32extends into the conductor portion 46 preferably in a range from about500 to 3,500 angstroms. The conductor portion 46 typically has athickness in a range of about 3,500 to 5,500 angstroms. The exact depthat which the anchor portion 22 extends into the conductor portion 46 isnot critical as long as the anchor portion 22 extends deep enough intothe conductor portion to provide sufficient strength to lock the bodyportion 34 of the metal plug 32 into place.

As previously discussed, the capacitance of the capacitor 20 isincreased by forming a trench 30 in the first dielectric layer 28. Thebody portion 34 of the metal plug 32 extends upwardly in a medialportion of the trench 30. The trench 30 is patterned, e.g., byconventional etching or other suitable techniques. For example, an etchstop 66 (FIG. 5), such as silicon nitride, is formed within the firstdielectric layer 28 during its formation. Accordingly, the etch stop 66determines the actual depth d of the trench 30. A method of making theintegrated circuit capacitor 20 including the anchor portion 22 of themetal plug 32 will be discussed in greater detail below.

With only a body portion 34 of the metal plug 32, i.e., no anchorportion 22, the depth d of the trench 30 is typically limited to abouthalf the thickness of the first dielectric layer 28. If the firstdielectric layer 28 has a thickness in a range of about 4,000 to 6,000angstroms, the depth d of the trench 30 would not exceed 2,000 to 3,000angstroms. However, with the anchor portion 22 locking the body portion34 of the metal plug 32 adjacent the lower portions of the firstdielectric layer 28, the depth d of the trench 30 can be greater thanhalf the thickness of the first dielectric layer. Accordingly, theincreased depth d of the trench 30 can now be in a range of about 2,000to 5,500 angstroms.

Once the trench 30 has been formed, the capacitor 20 is then formed. Thefirst electrode 36 lines the trench 30 and contacts the metal plug 32.The first electrode 36 is made from any material suitable for conductingand holding an electric charge. Suitable materials include titanium,titanium nitride, aluminum, copper, silver or noble metals such as gold,platinum and/or palladium. The thickness of the first electrode 36 ispreferably in a range of about 75 to 750 angstroms. It is also possiblefor the first electrode 36 to have a multi-layered arrangement, e.g., alayer of titanium coated with a layer of titanium nitride.

The second dielectric layer 38 overlies the first electrode 36 and isformed from any suitable dielectric, e.g., silicon dioxide, siliconnitride and/or any material or alloy of material having a suitably largedielectric constant. Other suitable materials include tantalum pentoxideand barium strontium titantate. The thickness of the second dielectriclayer 38 is preferably in a range of about 25 to 250 angstroms.

The second electrode 40 overlies the second dielectric layer 38. Likethe first electrode 36, the second electrode 40 is capable of being madefrom any material suitable for conducting and holding an electriccharge. The thickness of the second electrode 40 is preferably in arange of about 150 to 2,500 angstroms. It is also possible for thesecond electrode 40 to have a multi-layered arrangement, or even anarrangement whereby a first material, such as aluminum, is doped with asecond material, such as copper or silicon.

A method for making the integrated circuit capacitor 20 including ametal plug 32 as described above will now be further discussed withreference to FIGS. 2-5. A dielectric layer 42 may be formed, forexample, on a semiconductor substrate 24. The semiconductor substrate 24is preferably silicon, or may be silicon or a polysilicon layer orstructure formed on the substrate. A plurality of devices, such astransistors (not shown), are formed in the substrate 24 using well knowntechniques. Next, the dielectric layer 42, such as a doped or undopedsilicon dioxide, is formed over the substrate 24 with well knowntechniques, such as being thermally grown or being deposited.

Next, the interconnection line 26 is formed on the dielectric layer 42.In formation of the interconnection line 26, a titanium layer 48 ofapproximately 250 angstroms is formed over the dielectric layer 42 usingwell known techniques, such as sputtering. Although a titanium layer ispreferred, other refractory metal layers can be used. An approximately4,500 angstrom thick aluminum alloy layer 46 comprising approximately 1%copper is formed on the titanum layer using well known techniques, suchas sputtering. The aluminum alloy layer 46 is also referred to as theconductor portion. Although an aluminum alloy layer is preferred becauseof its low resistivity and its well known processes, other lowresistance materials may act as the conductor portion 46 in theinterconnection line 26, as will be appreciated by one skilled in theart. A layer of titanium 44 approximately 250 angstroms thick is formedon the conductor portion 46 by sputtering. Although titanium ispreferred, other refractory metal layers may be used. An anti-reflectivecoating 50, such as titanium nitride, is formed over the titanium layer44.

The first dielectric layer 28, such as a doped silicon dioxide, isformed over the interconnection line 26 Any well known technique can beused to form the first dielectric layer 28, such as chemical vapordeposition (CVD). The first dielectric layer 28 is preferably planarizedat this time by chemical-mechanical polishing or by etch back to form aplanar top surface. The resulting thickness of the first dielectriclayer 28 should be thick enough after planarization to provide adequateelectrical isolation of the interconnection line 26 from a subsequentlevel of metalization. An approximate thickness of 4,000 to 6,000angstroms for the first dielectric layer 28 provides suitable isolation.

A photoresist layer (not shown) is formed and patterned over the firstdielectric layer 28 using well known photolithography techniques todefine the location where the via 60 is to be formed. Next, the exposedportions of the first dielectric layer 28, the titanium nitride layer50, and the titanium layer 44 are etched. The via 60 is etched until thealuminum conductor portion 46 is exposed, as shown in FIG. 2. In oneembodiment, a reactive ion etch (RIE) is used to form the via 60.

Referring now to FIG. 3, the anchor hole 62 is formed in the aluminumconductor portion 46 of the interconnection line 26 using an isotropicwet etch. The isotropic wet etch is highly selective to the conductorportion 46 with respect to the capping layer 44. In other words, theconductor portion 46 is etched at a faster rate than the capping layer44. In this way, the conductor portion 46 is laterally etched awaybeneath the capping layer 44 forming a convex shape, which undercuts thecapping layer. The enlarged width portion 23 of the anchor portion 22undercuts beneath the capping layer preferably in a range of about 100to 600 angstroms. Other techniques may be utilized for forming theanchor hole 62, including a dry etching technique such as reactive ionetching (RIE), and plasma etching can be used, as will be appreciated byone skilled in the art.

Referring now to FIG. 4, the via 60 is filled with a conductivematerial, preferably tungsten, using well known techniques for formingthe metal plug 32. The anchor and body portions 22, 34 of the metal plug32 are integrally formed as a monolithic unit. Prior to forming themetal plug 32, a thin adhesion/barrier layer, such as titanium ortitanium nitride (not shown), are blanket deposited over the firstdielectric layer 28 and into the via 60 and the anchor hole 62 usingwell known techniques, such as sputtering. The conductive material ofthe metal plug 32 is then deposited into the via 60 until the anchorhole and via 62, 60 are filled. A chemical-mechanical polishingtechnique is used to etch back the adhesion/barrier metals and theconductive material deposited on the first dielectric layer 28. Otherwell known etch back techniques can be used, such as reactive ionetching (RIE).

A trench 30 is now formed adjacent the metal plug 32, as best shown inFIG. 5. The trench 30 is formed by patterning adjacent the metal plug 32using conventional etching or other suitable techniques. For example, asilicon nitride etch stop 66 is formed within the first dielectric layer28 during its formation. Accordingly, the etch stop 66 determines theactual depth d of the trench 30. Because the metal plug 32 is anchoredadjacent the lower portions of the first dielectric layer 28,positioning of the etch stop 66 can be greater without the metal plugbecoming loose and separating from the underlying interconnection line26, This advantageously allows the capacitance of the capacitor 20 to beincreased because of the increased surface area available for formingthe capacitor.

Once the trench 30 has been formed, the first electrode 36 of thecapacitor 20 is formed by depositing an electrically conductive materialon the first dielectric layer 28, including the trench 30 and the metalplug 32. Methods of depositing the first electrode 36 may includesputtering, reactive sputter etching (RSE), chemical vapor deposition(CVD) and plasma enhanced chemical vapor deposition (PECVD). The firstelectrode 36 is then selectively patterned.

The second dielectric layer 38 is deposited over the first electrode 36and patterned using an appropriate technique. The second dielectriclayer 38 may be deposited using CVD or any of the other techniquessimilar those used for depositing the first electrode 36. The secondelectrode 40 is then selectively patterned by an appropriate patterningtechnique. The capacitor 20 thus includes the first and secondelectrodes 36, 40 and the second dielectric layer 38 therebetween, asshown in FIG. 1.

As an alternative to forming the capacitor 20 comprising the seconddielectric layer 38 between the lower and upper electrodes 36, 40, thelower electrode is replaced by the upper portion of the metal plug 32.In other words, the upper portion of the metal plug 32 forms the lowerelectrode for the capacitor 20, as readily understood by one skilled inthe art.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that modificationsand embodiments are intended to be included within the scope of theappended claims.

That which is claimed is:
 1. An integrated circuit capacitorcomprising:a substrate; a first dielectric layer adjacent said substrateand having a trench therein; a metal plug comprisinga body portionextending upwardly into the trench, and an anchor portion connected tosaid body portion and having an enlarged width portion to anchor saidmetal plug adjacent lower portions of said first dielectric layer; asecond dielectric layer adjacent an upper portion of said metal plug andextending downwardly into the trench; and an electrode on said seconddielectric layer.
 2. An integrated circuit capacitor according to claim1, further comprising an electrode between said metal plug and saidsecond dielectric layer.
 3. An integrated circuit capacitor according toclaim 1, wherein said body portion and said anchor portion areintegrally formed as a monolithic unit.
 4. An integrated circuitcapacitor according to claim 1, wherein said enlarged width portion hasa convex shape.
 5. An integrated circuit capacitor according to claim 1,wherein the trench has a depth greater than about half a thickness ofsaid first dielectric layer.
 6. An integrated circuit capacitoraccording to claim 1, wherein said enlarged width portion of said anchorportion is greater than about 10% of a width of said body portion.
 7. Anintegrated circuit capacitor according to claim 1, wherein a depth ofthe trench is greater than about 2000 angstroms.
 8. An integratedcircuit capacitor according to claim 1, further comprising aninterconnection line extending below said first dielectric layer andconnected to said metal plug.
 9. An integrated circuit capacitoraccording to claim 1, wherein said body portion of said metal plug hasan uppermost surface substantially co-planar with an adjacent uppermostsurface of said first dielectric layer.
 10. An integrated circuitcapacitor according to claim 1, wherein said metal plug comprisestungsten.
 11. An integrated circuit capacitor according to claim 1,wherein said body portion of said metal plug extends upwardly in amedial portion of the trench.
 12. An integrated circuit capacitorcomprising:a substrate; an interconnection line adjacent said substrate;a first dielectric layer on said interconnection line and having atrench therein; a metal plug comprisinga body portion extending upwardlyinto the trench, and an anchor portion connected to said body portionand extending into said interconnection line, said anchor portion havingan enlarged width portion to anchor said metal plug adjacent lowerportions of said first dielectric layer; a second dielectric layeradjacent an upper portion of said metal plug and extending downwardlyinto the trench; and an electrode on said second dielectric layer. 13.An integrated circuit capacitor according to claim 12, furthercomprising an electrode between said metal plug and said seconddielectric layer.
 14. An integrated circuit capacitor according to claim12, wherein said body portion and said anchor portion are integrallyformed as a monolithic unit.
 15. An integrated circuit capacitoraccording to claim 12, wherein said enlarged width portion has a convexshape.
 16. An integrated circuit capacitor according to claim 12,wherein the trench has a depth greater than about half a thickness ofsaid first dielectric layer.
 17. An integrated circuit capacitoraccording to claim 12, wherein said enlarged width portion of saidanchor portion is greater than about 10% of a width of said bodyportion.
 18. An integrated circuit capacitor according to claim 12,wherein a depth of the trench is greater than about 2000 angstroms. 19.An integrated circuit capacitor according to claim 12, wherein said bodyportion of said metal plug has an uppermost surface substantiallyco-planar with an adjacent uppermost surface of said first dielectriclayer.
 20. An integrated circuit capacitor according to claim 12,wherein said metal plug comprises tungsten.
 21. An integrated circuitcapacitor according to claim 12, wherein said body portion of said metalplug extends upwardly in a medial portion of the trench.
 22. Anintegrated circuit capacitor comprising:a substrate; a first dielectriclayer adjacent said substrate and having a trench therein, the trenchhaving a depth greater than about half a thickness of said firstdielectric layer; a metal plug comprisinga body portion extendingupwardly into the trench, and an anchor portion connected to said bodyportion and having a convex-shaped enlarged width portion to anchor saidmetal plug adjacent lower portions of said first dielectric layer; asecond dielectric layer adjacent an upper portion of said metal plug andextending downwardly into the trench; and an electrode on said seconddielectric layer.
 23. An integrated circuit capacitor according to claim22, further comprising an electrode between said metal plug and saidsecond dielectric layer.
 24. An integrated circuit capacitor accordingto claim 22, wherein said body portion and said anchor portion areintegrally formed as a monolithic unit.
 25. An integrated circuitcapacitor according to claim 22, wherein said convex-shaped enlargedwidth portion of said anchor portion is greater than about 10% of awidth of said body portion.
 26. An integrated circuit capacitoraccording to claim 22, wherein a depth of the trench is greater thanabout 2000 angstroms.
 27. An integrated circuit capacitor according toclaim 22, further comprising an interconnection line extending belowsaid first dielectric layer and connected to said metal plug.
 28. Anintegrated circuit capacitor according to claim 22, wherein said bodyportion of said metal plug has an uppermost surface substantiallyco-planar with an adjacent uppermost surface of said first dielectriclayer.
 29. An integrated circuit capacitor according to claim 22,wherein said metal plug comprises tungsten.
 30. An integrated circuitcapacitor according to claim 22, wherein said body portion of said metalplug extends upwardly in a medial portion of the trench.